To those of us with the unenviable task of following the seemingly endless US presidential campaign, the election last Tuesday ended with something of a whimper. The trajectory of the race has been clear since practically the spring. President Obama held a narrow but persistent lead in national polls and a broader lead in the all-important electoral college. That was precisely the result on election night.

But what was more surprising about election night was not that Obama won, but rather the breadth of the victory for the Democratic party. The verdict of the American people confirms what has been hazily evident for some time, but now is in even sharper relief: the Democrats are the dominant presidential party in US politics, and not just in politics but in the policy realm as well.

Democrats, who last night added Florida to their list of swing-state victories, have now won the popular vote in five of the last six presidential elections (even if they only won four of them). While Republicans have failed to crack 300 electoral votes since 1988, the Democrats are now winning elections in states where they were barely competitive just a few cycles ago. The early verdict among political pundits as to why Democrats are enjoying such success centres around demographics.

There is much to this argument. Democrats lost the white vote on Tuesday by a whopping 20 points – a similar disadvantage to when they were crushed in the 1988 election. The difference is that today African Americans and Hispanics are a far larger share of the population and they overwhelmingly support the Democratic party. In Virginia, for example, a state that was once solidly Republican, Obama lost whites by 24 points but an astonishing 87-point advantage among African Americans was enough to eke out a narrow win.

The changing racial makeup of the US has transformed American politics and given Democrats an enormous electoral advantage. Throw in the fact that socially liberal young voters, along with unmarried women, are overwhelmingly in their camp and Democrats have created a broad-based political coalition. As was the case last Tuesday, Republicans have for decades relied on the overwhelming support of white voters (particularly southerners, evangelicals, rural residents and senior citizens) and their abundant cultural anxieties, frustrations and resentments. That strategy appears to have run its course. In a year in which their standard-bearer made little serious effort to reach out to minority voters and at times fanned the flames of racial animus, it's a compelling indication that a white-centric political strategy is no longer a route to success.

Of course, demography can be a fleeting thing and one day Democrats could, as they have in the past, find themselves on the wrong side of this divide. That's why last Tuesday's results are so important; this was more than a demographic win, it was a policy one as well.

Take, for example, immigration. During the 2012 campaign, Republicans resisted any discussion of providing illegal immigrants with a path to citizenship. But after losing the Hispanic vote by stunningly large margins – and seeing a strong majority of all Americans opposed to their enforcement-only approach – Republicans have shifted course and are now talking up the need for compromise on the issue.

Four states voted on the question of gay marriage last Tuesday, and in each the pro-marriage equality side won, suggesting that an issue which eight years ago served as a cudgel for Republicans to push so-called "cultural" voters to the polls is no longer a political asset. Indeed, the Grand Old Party barely talks about gay marriage now, while Democrats are making it a key feature of messaging on social issues. Finally, there is abortion – an issue that bedevilled two of the GOP's Senate candidates, Todd Akin and Richard Mourdock, because they found it difficult to reconcile their extreme anti-abortion views with the question of whether pregnant rape victims should be able to get an abortion. They came down against it – and sowed the seeds of their political demise. Combine a harsh line on abortion with increasingly vocal opposition to contraception access, and a rather Darwinian world view on social safety nets, it is small wonder that Obama trounced Romney among female voters.

And it's not just social policy. One of Obama's key economic messages was his call for wealthy Americans to pay more in taxes. It's an argument that he decisively won. Among voters who believed Americans making above $250,000 (£157,000) should pay more in taxes, 70% of them voted for Obama. But what is far worse for Republicans is that even as 76% of the country said the economy was doing either "not good" or "poorly", Obama and Romney were tied on the question of who Americans thought would do a better job of handling it. Exit polls showed the same result on the deficit. The exploding levels of budgetary red ink and Obama's supposedly failed stewardship of the economy were Romney's key anti-Obama talking points. That he could score only a draw on them is remarkable: a telling indication that his economic arguments simply didn't resonate.

The reason why may come from another exit poll result. Among the fifth of voters who said the most important quality to them in choosing a candidate was "cares about people like me", Obama had a whopping 81-18 edge. This was undoubtedly a consequence of the vulture capitalist, overseas job-shipping, Cayman Islands tax-haven image that the Obama campaign stamped on Romney; but it is also a result of Republicans being seen as a political party more interested in plutocrats than the middle class.

In the end, Republicans didn't just lose a presidential election or seats in Congress. After four years of pitched battle with the White House, they lost the war of ideas. If there is any one decisive result to take away from Tuesday night it is that, even in the face of high unemployment and sluggish economic growth, voters had more confidence in Democrats to turn things around than they did Republicans. Beyond that, they appear to see Democrats as the party on their side. This doesn't mean we've entered a period of political realignment but suggests national debates on social and economic policy are being waged on Democratic, even liberal, turf. That is an unexpected result, with consequences that will probably endure far past election day.